PCI: tegra: make const array err_msg static

Don't populate the array err_msg on the stack but instead make it
static. Makes the object code smaller by 64 bytes.

While at it, add a missing const, as reported by checkpatch.

Compiled with gcc 11.0.1

Before:
$ size drivers/pci/controller/pci-tegra.o
   text	   data	    bss	    dec	    hex	filename
  25623	   2844	     32	  28499	   6f53	drivers/pci/controller/pci-tegra.o

After:
$ size drivers/pci/controller/pci-tegra.o
   text	   data	    bss	    dec	    hex	filename
  25559	   2844	     32	  28435	   6f13	drivers/pci/controller/pci-tegra.o

Link: https://lore.kernel.org/r/5f3f35296b944b94546cc7d1e9cc6186484620d8.1620148539.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Vidya Sagar <vidyas@nvidia.com>