drm/i915: fix a couple of spelling mistakes in kernel parameter help text

There are a couple of spelling mistakes in kernel parameter help text,
namely "helpfull" and "paramters".  Fix them.
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200616082129.65517-1-colin.king@canonical.com

drivers/gpu/drm/i915/i915_params.c

@@ -99,8 +99,8 @@ i915_param_named_unsafe(enable_psr, int, 0400,
 
 i915_param_named(psr_safest_params, bool, 0400,
 	"Replace PSR VBT parameters by the safest and not optimal ones. This "
-	"is helpfull to detect if PSR issues are related to bad values set in "
-	" VBT. (0=use VBT paramters, 1=use safest parameters)");
+	"is helpful to detect if PSR issues are related to bad values set in "
+	" VBT. (0=use VBT parameters, 1=use safest parameters)");
 
 i915_param_named_unsafe(force_probe, charp, 0400,
 	"Force probe the driver for specified devices. "