net: Fix an ignored error return from dm9051_get_regs()

The return from the call to dm9051_get_regs() is int, it can be
a negative error code, however this is being assigned to an unsigned
int variable 'ret', so making 'ret' an int.

Eliminate the following coccicheck warning:
./drivers/net/ethernet/davicom/dm9051.c:527:5-8: WARNING: Unsigned
expression compared with zero: ret < 0

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220216014507.109117-1-yang.lee@linux.alibaba.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>