doc: imx: habv4: Fix typo in 'signing'

Fix two occurrences where 'signing' is misspelled.

Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Tim Harvey <tharvey@gateworks.com>
diff --git a/doc/imx/habv4/guides/mx6_mx7_secure_boot.txt b/doc/imx/habv4/guides/mx6_mx7_secure_boot.txt
index 53f71fb..7fba84a 100644
--- a/doc/imx/habv4/guides/mx6_mx7_secure_boot.txt
+++ b/doc/imx/habv4/guides/mx6_mx7_secure_boot.txt
@@ -113,7 +113,7 @@
 1.4 Signing the U-Boot binary
 ------------------------------
 
-The CST tool is used for singing the U-Boot binary and generating a CSF binary,
+The CST tool is used for signing the U-Boot binary and generating a CSF binary,
 users should input the CSF description file created in the step above and
 should receive a CSF binary, which contains the CSF commands, SRK table,
 signatures and certificates.
diff --git a/doc/imx/habv4/guides/mx6_mx7_spl_secure_boot.txt b/doc/imx/habv4/guides/mx6_mx7_spl_secure_boot.txt
index fde0f27..56b8cd6 100644
--- a/doc/imx/habv4/guides/mx6_mx7_spl_secure_boot.txt
+++ b/doc/imx/habv4/guides/mx6_mx7_spl_secure_boot.txt
@@ -145,7 +145,7 @@
 1.4 Signing the images
 -----------------------
 
-The CST tool is used for singing the U-Boot binary and generating a CSF binary,
+The CST tool is used for signing the U-Boot binary and generating a CSF binary,
 users should input the CSF description file created in the step above and
 receive a CSF binary, which contains the CSF commands, SRK table, signatures
 and certificates.