bnxt_en: Refactor bnxt_get_regs()

bnxt_en: Refactor bnxt_get_regs()

Separate the code that sends the FW message to retrieve pcie stats into
a new helper function.  The caller of the helper will call hwrm_req_hold()
beforehand and so the caller will call hwrm_req_drop() in all cases
afterwards.  This helper will be useful when adding the support for the
larger struct pcie_ctx_hw_stats_v2.

Signed-off-by: Shruti Parab <shruti.parab@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Link: https://patch.msgid.link/20250819163919.104075-3-michael.chan@broadcom.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>