The mountmsdosfs() function had an insane sanity test, remove it.

The mountmsdosfs() function had an insane sanity test, remove it.

Trying FAT32 on a small partition failed to mount because
pmp->pm_Sectors was nonzero.  Normally, FAT32 file systems are so
large that the 16-bit pm_Sectors can't hold the size.  This is
indicated by setting it to 0 and using only pm_HugeSectors.  But at
least old versions of newfs_msdos use the 16-bit field if possible,
and msdosfs supports this except for breaking its own support in the
sanity check.  This is quite different from the handling of pm_FATsecs
-- now the 16-bit value is always ignored for FAT32 except for
checking that it is 0, and newfs_msdos doesn't use the 16-bit value
for FAT32.

Submitted by:	bde
MFC after:	1 week