build: rename dependency variable

Per [1], the conventions for dependency variables are to
be named '<project or lib>_dep'.  This allows consistency
when using this project as a meson-subproject elsewhere.

Switch the name from 'libpldm' to 'libpldm_dep'.

1. https://mesonbuild.com/Subprojects.html#naming-convention-for-dependency-variables

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I98c8e2148610b45755b45029d1d38206bac5b885
diff --git a/meson.build b/meson.build
index dcb0e44..63bb198 100644
--- a/meson.build
+++ b/meson.build
@@ -63,7 +63,7 @@
   'common/utils.cpp',
   version: meson.project_version(),
   dependencies: [
-      libpldm,
+      libpldm_dep,
       phosphor_dbus_interfaces,
       sdbusplus,
   ],
@@ -77,7 +77,7 @@
 subdir('libpldmresponder')
 
 deps = [
-  libpldm,
+  libpldm_dep,
   libpldmutils,
   libpldmresponder,
   libpldmutils,