We get this on 32 builds:

fs/built-in.o: In function `extent_fiemap':
(.text+0x1019f2): undefined reference to `__ucmpdi2'

Happens because of a switch statement with a 64 bit argument.
Convert this to an if statement to fix this.
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NChris Mason <chris.mason@oracle.com>