net: jme: remove unused initialization of 'rxdesc'

Pointer rxdesc is assigned a value that is never read, it is overwritten
by a new assignment inside a while loop hence the initial assignment
is redundant and can be removed.

Cleans up clang warning:
drivers/net/ethernet/jme.c:1074:17: warning: Value stored to 'rxdesc'
during its initialization is never read

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>