drivers: remoteproc: rproc-uclass: Fix check for NULL pointers

Neither uc_pdata->name nor check_name are supposed to be NULL in
_rproc_name_is_unique(). if uc_pdata->name is NULL, we are not
intialized yet, however if check_data is NULL, we do not have
proper data. Further, if either were NULL, strlen will crap out
while attempting to derefence NULL.

Instead, just check if either of these are NULL and bail out.

This should also fix the following coverity scan warnings:
*** CID 132281:  Null pointer dereferences  (FORWARD_NULL)
/drivers/remoteproc/rproc-uclass.c: 73 in _rproc_name_is_unique()

Reported-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Nishanth Menon <nm@ti.com>