bus: fsl-mc-msi: Fix MSI descriptor mutex lock for msi_first_desc()

Commit e8604b14 introduced a call to the helper function
msi_first_desc(), which needs MSI descriptor mutex lock before
call. However, the required mutex lock was not added. This results in
lockdep assertion:

 WARNING: CPU: 4 PID: 119 at kernel/irq/msi.c:274 msi_first_desc+0xd0/0x10c
  msi_first_desc+0xd0/0x10c
  fsl_mc_msi_domain_alloc_irqs+0x7c/0xc0
  fsl_mc_populate_irq_pool+0x80/0x3cc

Fix this by adding the mutex lock and unlock around the function call.

Fixes: e8604b14 ("bus: fsl-mc-msi: Simplify MSI descriptor handling")
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20220412075636.755454-1-shinichiro.kawasaki@wdc.com

drivers/bus/fsl-mc/fsl-mc-msi.c

@@ -224,8 +224,12 @@ int fsl_mc_msi_domain_alloc_irqs(struct device *dev,  unsigned int irq_count)
 	if (error)
 		return error;
 
+	msi_lock_descs(dev);
 	if (msi_first_desc(dev, MSI_DESC_ALL))
-		return -EINVAL;
+		error = -EINVAL;
+	msi_unlock_descs(dev);
+	if (error)
+		return error;
 
 	/*
 	 * NOTE: Calling this function will trigger the invocation of the