bus: mhi: pci_generic: Add mru_default for Quectel EM1xx series

bus: mhi: pci_generic: Add mru_default for Quectel EM1xx series

For default mechanism, the driver uses default MRU 3500 if mru_default
is not initialized. The Qualcomm configured the MRU size to 32768 in the
WWAN device FW. So, we align the driver setting with Qualcomm FW setting.

Fixes: ac4bf60bbaa0 ("bus: mhi: pci_generic: Introduce quectel EM1XXGR-L support")
Signed-off-by: Yonglin Tan <yonglin.tan@outlook.com>
Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/MEYP282MB2374EE345DADDB591AFDA6AFFD2E9@MEYP282MB2374.AUSP282.PROD.OUTLOOK.COM
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>