hwrng: amd - Convert PCIBIOS_* return codes to errnos

amd_rng_mod_init() uses pci_read_config_dword() that returns PCIBIOS_*
codes. The return code is then returned as is but amd_rng_mod_init() is
a module_init() function that should return normal errnos.

Convert PCIBIOS_* returns code using pcibios_err_to_errno() into normal
errno before returning it.

Fixes: 96d63c02 ("[PATCH] Add AMD HW RNG driver")
Cc: stable@vger.kernel.org
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>