fix(tree): correct some typos

found using codespell (https://github.com/codespell-project/codespell).

Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Change-Id: I1bfa797e3460adddeefa916bb68e22beddaf6373
diff --git a/plat/rpi/rpi4/rpi4_pci_svc.c b/plat/rpi/rpi4/rpi4_pci_svc.c
index 7d1ca5c..e4ef5c1 100644
--- a/plat/rpi/rpi4/rpi4_pci_svc.c
+++ b/plat/rpi/rpi4/rpi4_pci_svc.c
@@ -11,7 +11,7 @@
  * it. Given that it's not ECAM compliant yet reasonably simple, it makes for
  * an excellent example of the PCI SMCCC interface.
  *
- * The PCI SMCCC interface is described in DEN0115 availabe from:
+ * The PCI SMCCC interface is described in DEN0115 available from:
  * https://developer.arm.com/documentation/den0115/latest
  */