mount.nfs: Eliminate compiler warnings

Clean up.

fstab.c: In function ?lock_mtab?:
fstab.c:385: warning: declaration of ?errsv? shadows a previous local
fstab.c:367: warning: shadowed declaration is here
fstab.c:407: warning: declaration of ?errsv? shadows a previous local
fstab.c:367: warning: shadowed declaration is here
fstab.c:417: warning: declaration of ?tries? shadows a previous local
fstab.c:325: warning: shadowed declaration is here
fstab.c:422: warning: declaration of ?errsv? shadows a previous local
fstab.c:367: warning: shadowed declaration is here

These are probably harmless.  Reusing a variable name, however, is a
little confusing to follow when reading the code.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>