[ATM]: Fix compiler warning noise with FORE200E driver

gcc throws these warnings with:

CONFIG_ATM_FORE200E=m
# CONFIG_ATM_FORE200E_PCA is not set

drivers/atm/fore200e.c:2695: warning: 'fore200e_pca_detect' defined but
not used
drivers/atm/fore200e.c:2748: warning: 'fore200e_pca_remove_one' defined
but not used

By moving the #ifdef CONFIG_ATM_FORE200E_PCA around those two functions,
the compiler warnings are silenced.

Signed-off-by: Tom "spot" Callaway <tcallawa@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>