fsmgr: fix integer overflow in fs_mgr

As the EXT4_MAX_BLOCK_SIZE defined as 65536 which reached maxium value
of unsigned int. The superblock value maybe larger than 65536. This is
found by the Integer Overflow Sanitizer.

This patch fixed below boot error when userdata is corrupted:
init: processing action (fs) from
(/vendor/etc/init/hw/init.freescale.rc:221)
init: [libfs_mgr]Invalid ext4 superblock on '/dev/block/by-name/userdata'
init: InitFatalReboot: signal 6 init: #00 pc 00000000000af7e8  /system/bin/init
(android::init::InitFatalReboot(int)+208) init: #01 pc 00000000000afbd0  /system/bin/init
(android::init::InstallRebootSignalHandlers()::$_22::__invoke(int)+32)
init: #02 pc 00000000000006bc  [vdso:0000ffff9691b000] (__kernel_rt_sigreturn)
init: #03 pc 000000000004e070  /system/lib64/bootstrap/libc.so (abort+176)
init: #04 pc 000000000003427c  /system/lib64/libfs_mgr.so
(read_ext4_superblock(std::__1::basic_string<char, std::__1::char_
traits<char>, std::__1::allocator<char> > const&,
android::fs_mgr::FstabEntry const&, ext4_super_block*, int*)+1804)

Test: boot with corrupted ext4 superblock
Bug: 156200421

Signed-off-by: Haoran.Wang <elven.wang@nxp.com>
Change-Id: Ib1b69bf4623f69696cb637b226ec3359fc2ed409
(cherry picked from commit cb472b92e54ba1647c02397565958322f0d74929)

Former-commit-id: e28dc48de52af3e216fb3a85df382f3643b39496

fs_mgr/fs_mgr.cpp

@@ -331,7 +331,7 @@ static bool read_ext4_superblock(const std::string& blk_device, const FstabEntry
             // try backup superblock, if main superblock is corrupted
             for (unsigned int blocksize = EXT4_MIN_BLOCK_SIZE; blocksize <= EXT4_MAX_BLOCK_SIZE;
                  blocksize *= 2) {
-                unsigned int superblock = blocksize * 8;
+                uint64_t superblock = blocksize * 8;
                 if (blocksize == EXT4_MIN_BLOCK_SIZE) superblock++;
 
                 if (TEMP_FAILURE_RETRY(pread(fd, sb, sizeof(*sb), superblock * blocksize)) !=