firmware: arm_ffa: Use the correct buffer size during RXTX_MAP

Don't use the discovered buffer size from an FFA_FEATURES call directly
since we can run on a system that has the PAGE_SIZE larger than the
returned size which makes the alloc_pages_exact for the buffer to be
rounded up.

Fixes: 61824fe ("firmware: arm_ffa: Fetch the Rx/Tx buffer size using ffa_features()")
Signed-off-by: Sebastian Ene <sebastianene@google.com>
Link: https://patch.msgid.link/20260402113939.930221-1-sebastianene@google.com
Signed-off-by: Sudeep Holla <sudeep.holla@kernel.org>

Author: Sebastian Ene

drivers/firmware/arm_ffa/driver.c

@@ -2078,7 +2078,7 @@ static int __init ffa_init(void)
 
 	ret = ffa_rxtx_map(virt_to_phys(drv_info->tx_buffer),
 			   virt_to_phys(drv_info->rx_buffer),
-			   rxtx_bufsz / FFA_PAGE_SIZE);
+			   PAGE_ALIGN(rxtx_bufsz) / FFA_PAGE_SIZE);
 	if (ret) {
 		pr_err("failed to register FFA RxTx buffers\n");
 		goto free_pages;